1. Field of the Invention
The present invention relates to a disk control apparatus having a device adapter circuit connected to an internal bus, and, more particularly, to a disk control apparatus capable of accomplishing parallel data transfer from a plurality of disk devices.
2. Description of the Related Art
Disk storage systems like a magnetic disk system are employed as an external memory device in a computer system. A disk storage system has a plurality of magnetic disk devices and a disk control apparatus which controls those disk devices. The disk control apparatus accesses a designated magnetic disk device in response to an access request from a high-rank apparatus.
When the magnetic disk device is ready to be accessed, it gives a notice to the disk control apparatus. Then, the magnetic disk device starts transferring data to the disk control apparatus. The disk control apparatus transfers that data to the high-rank apparatus. Efficient control of data transfer is demanded of such a disk control apparatus.
FIG. 10 is a block diagram of a prior art disk control apparatus.
As shown in FIG. 10, a disk control apparatus 80 is connected to a plurality of magnetic disk devices 90-1 to 90-4. The disk control apparatus 80 comprises a channel adapter circuit 81, a resource manager circuit 82, a table storage 83, a main storage 84, a device adapter circuit 85 and an internal bus 86.
The channel adapter circuit 81 controls interface with a high-rank apparatus. The resource manager circuit 82 manages resources. The table storage 83 stores various kinds of tables for the resource management by the resource manager circuit 82.
The main storage 84 temporarily stores read data from a magnetic disk device. The device adapter circuit 85 accesses any designated one of the magnetic disk devices 90-1 to 90-4 and transfers data to the main storage 84.
The operation of this disk control apparatus 80 will be described below. When receiving an access request from a high-rank apparatus, the channel adapter circuit 81 notifies that access request to the resource manager circuit 82. The resource manager circuit 82 assigns an area in the main storage 84, then requests the device adapter circuit 85 to access the designated one of the magnetic disk devices 90-1 to 90-4.
The device adapter circuit 85 accesses the designated magnetic disk device 90-1, 90-2, 90-3 or 90-4. When the designated magnetic disk device 90-1, 90-2, 90-3 or 90-4 becomes ready to transfer data, it gives a notice to that effect to the device adapter circuit 85. Then, that magnetic disk device 90-1, 90-2, 90-3 or 90-4 transfers data to the device adapter circuit 85.
After getting a permission to use the internal bus 86, the device adapter circuit 85 transfers the data to the main storage 84. When receiving a notice of the end of data transfer from the device adapter circuit 85, the resource manager circuit 82 instructs the channel adapter circuit 81 to start data transfer. After acquiring the permission to use the internal bus 86, the channel adapter circuit 81 reads data from the main storage 84. Then, the channel adapter circuit 81 transfers the data to the high-rank apparatus.
FIG. 11 is a structural diagram of the prior art device adapter circuit, and FIG. 12 is an explanatory diagram of the prior art. FIG. 11 shows the internal structure of the device adapter circuit 85.
As shown in FIG. 11, the device adapter circuit 85 has a bus interface circuit 87, an automatic transfer circuit 88 and a data transfer circuit 89.
The bus interface circuit (BIL) 87, connected to the internal bus 86, performs interface control on the internal bus 86. The automatic transfer circuit (ADT) 88 accesses the magnetic disk devices 90-1 to 90-4 via the data transfer circuit (SCSI) 89 in accordance with an access request from the interface circuit 87.
When any of the magnetic disk devices 90-1 to 90-4 becomes ready for data transfer, it notifies such to the automatic transfer circuit 88. The automatic transfer circuit 88 instructs the interface circuit 87 to get the permission to use the internal bus 86. The automatic transfer circuit 88 receives data from that one of the magnetic disk devices 90-1 to 90-4, then transfers it to the interface circuit 87. The interface circuit 87 transfers that data to the internal bus 86.
As shown in FIG. 12, the magnetic disk devices 90-1 to 90-4 transfer data in accordance with the transfer rate of each magnetic disk device. The interface circuit 87 transfers data to the internal bus in accordance with that transfer rate. The conventional device adapter 85 therefore starts the data transfer of one magnetic disk device after completing the data transfer of a previous magnetic disk device.
The transfer rate of each magnetic disk device however depends on the data reading speed of that magnetic disk device. Generally speaking, magnetic disk devices have a relatively low transfer rate. By contrast, the transfer rate of the internal bus is relatively fast because only electric control is involved. Actually, the transfer rate of the internal bus is more than two times faster than that of magnetic disk devices.
According to the conventional structure, the transfer rate of the internal bus is designed to match the transfer rate of magnetic disk devices. The prior art could not therefore effectively use the transfer rate of the internal bus.